Combustion test



Sept. 4, 1956 A. H. POPKIN 2,761,766

COMBUSTION TEST Filed May 1, 1953 Alexander H. Popkin Invemor By AAttorney United States Patent 2,761,766 COMBUSTION TEST Application May1, '1953,'Serlal N0. 352,373 9 Claims. (11. 23-230 The present inventionrelates to a new and improved method of testing the combustioncharacteristics of combustible materials. More particularly, theinvention is concerned with an improved method for testing the tendencyof such materials toward forming combustion chamber deposits when usedin the combustion chambers of internal combustion engines.

In brief compass, the invention pertains to a method for testing thedeposit-forming tendencies. of motor fuels, lubricants, aswell asadditives for fuels and lubricants by subjecting these materials tocombustion under a cleanburning flame, particularly a hydrogen flame ina container having smooth non-absorbing inner surfaces, to form a drycombustion residue on said surfaces. The quantity of total depositindicates certain properties of the material tested. Thereafter, thatportion of the deposit which adheres loosely to the surface may beremoved by light mechanical friction and the remaining firmlyadheringdeposit may be determined. By reference to correlated data it ispossible to rate the test material as to its combustion deposit-formingtendencies on the basis of the amount of total deposit and/or the amountof the loosely and/or firmly adhering portions thereof.

The problem of combustion chamber deposits is of urgent concern to theautomotive and oil industries. These deposits increase the octanerequirements of gasoline engines by about 10 octane units in 3,000 to5,000 miles. They may also cause preignition, a phenomenon which maylead to knock, and loss of power. As it is becoming increasinglydifficult to provide gasoline having the octane quality required by thenew high compression engines, it is important to eliminate or reduce theelfect of these deposits. 1,

Extensive studies have demonstrated that the formaf tion of combustionchamber deposits may be caused by the fuel, the lubricating oil, as wellas by additives used in either of these. A reliable method forpredicting the tendency of fuels, lubricants and additives to form suchdeposits is, therefore, urgently needed. Past field and laboratorystudies and the'correlation of their results have shown that none of theknown laboratory engine tests is suitable for this purpose.

The present invention provides this needed test in an extremely simpleand most reliable manner as will ap pear from the subsequent descriptionread with reference to the accompanying drawing, the single figure ofwhich of the vessel. In most cases conditions are so controlled that theflame enters the vessel over a distance of at least about 0.52 inches.

Usually within less than 2 minutes of exposure to the hydrogen flame thesample begins to burn. The hydrogen flame is continued until the sampleis completely burned and only a dry residue remains. Thereafter, thehydrogen flame is discontinued and the vessel is allowed to cool.

The amount of total combustion residue is now determined by weighing thevessel and deducting from its weight the weight of the empty vessel.This total deposit has been found to correlate satisfactorily with theoctane requirement increase determined in actual field tests for a largenumber of motor fuels.

Particularly in the case of testing lubricants, after determination ofthe total deposit, the interior of the vessel is carefully wiped with asoft material, such as cloth or soft wiping paper, until no furtherremoval of deposits from the vessel is obtained. Somewhat more effort isrequired in wiping carbonaceous deposits from the sides of the vessel inthe case of lubricant tests than in the case of fuel tests. Such wipingremoves carbon deposits. However, varnish which adheres tenaciously tothe smooth vessel wall is not removed by this treatment. After wiping,and preferably after a further short standing period for removing staticelectricity, the vessel is weighed again. The increase in weight of thewiped vessel over the emptiedvessel is the amount of varnish formed bythe sample and the diiference between the total deposit and varnishcorresponds to the amount of carbon and a substantial proportion of theash. The varnish deposits so obtained correlate satisfactorily with theoctane requirement increase obtained in actual field tests for a largenumber of lubricants. The loosely adhering carbon deposit may be readlyanalyzed to determine the character and proportion of the ashconstituents of the combustion chamber deposit.

In accordance with the invention, hydrogen is used in preference toother secondary fuels to obtain a clean flame which itself forms no Icarbonaceous combustion products. Certain other fuels, such as methane,ethane,

propane, etc., may be used provided combustion condiis a perspectiveview of equipment adapted to carry out p a preferred embodiment of theinvention.

In accordance with the present invention it hasbeen found that thecombustion residue remaining when burning an oil or fuel sample in ahydrogen flame under controlled conditions may serve accurately topredict the tendency of the sample material toward forming combustionchamber deposits in internal combustion engines. In carrying out thetest of the invention, the sample to :be tested is placed in an openvessel having smooth nonabsorptive inner surfaces, such as a glassbeaker, porcelain crucible, heat-resistant metal beaker or crucible,etc. 1

A clean burning hydrogen flame is then directed into the opening of thevessel. The position of the burner tip and the flow rates of hydrogenand oxygen should be so controlled that the flame is directed toward theinterior I,

tions are such as will provide a clean burning flame. The feed ratiobetween hydrogen and air to the flame of the invention may vary withinwide limits. However, some materials, particularly lubricants, mayrequire a hotter flame than others, in which case relatively high airratios may be employed.

While any burner type may be used provided hydrogen may be burned undercarefully controlled burning conditions, a conventional acetylene blowtorch type of burner is preferred. This type of burner affords thegreatest ease of control; of combustion mixture and flame length. Theuse of equipment of this type for the purposes of the invention isdiagrammatically illustrated in the drawing. V g

Referring now to the drawing, the numeral 1 designates a conventionalblow torch provided with air control valve 2, hydrogen control valve 3and mixing chamber 4. The torch tip 5 preferably has an opening of about0.125 in. diameter and is set at an angle of about 10-20 as indicated inthe drawing.

At a distance of about 6-7 inches below the tip of the torch, there isplaced the rim of a glass beaker 6 or other vessel with smoothnon-absorptive inner surfaces, containing the Sample 7 to be tested. Asindicated in the drawing, the flame enters the top of the beaker withouttouching its walls and ending at a distance above the level of thesample.

The application of the equipment illustrated in the drawing for thepurposes of the invention will now explained with the aid of specificexamples.

EXAMPLE I The following is a detailed procedure for the burning of asample of lubricant in accordance with the invention. A 250 cc. beakeris weighed on an analytical balance to the fourth decimal place. Intothe beaker are then added 5.000 grams grams) of lubricant using the sameanalytical balance. The beaker is then placed underthe burning hydrogentorch in the position indicated in the drawing. The tip of the torch is6 /2 inches from the top of the beaker and set at an angle as shown.This position and the flow rates of hydrogen (0.166 cu. ft./min.) andprimary air (0.116 cu. ft. per min.) are drawn to give a flame length ofabout 7 /2 inches, or a flame extending about one inch below the top ofthe beaker. The flame, moreover, is about M4 inch from the rear top ofthe beaker. The flame should not touch the rear portion of the beaker orextend to the bottom of the beaker.

The beaker and contents are placed under the flame in the designatedposition. Within one minute, vapors and/or slight burning will beobtained. At this time, spattering may also start due to the presence ofcondensed water formed from the hydrogen-air combustion in the hot oil.It is advisable, if spattering is noted, to lift the beaker slightlyfrom the support surface and to gently stir the lubricant sample by aslow rotary motion of the beaker until a continuous flame is obtained.This may require one-half to one minute of the rotary motion. When thesample begins to burn steadily, the beaker is replaced under the flameand burning continued until a flame is no longer obtained. The beaker isthen slowly turned 180 degrees during about 30 seconds to burn the highboiling residual liquid. At this stage, the beaker is removed from flameand the condition at the bottom of the beaker observed by tilting thebeaker. If liquid or vapor are noted, the beaker is placed under theflame for an additional 30 seconds and ob servation repeated. If noliquid is noted, and vapors are not evident in the beaker, the sample isset aside to cool. The total burning time may vary from 5-15 minutes,oils containing heavy ends (i. e., bright stock) requiring longerburning times.

Following the burning, the beaker is allowed to stand at roomtemperature for at least an hour before weighing. The increase in beakerweight is recorded as the total deposit. The carbon from the sides ofthe beaker is then removed with several wipings of a suitable softlaboratory wiping paper (e. g., large Kim-Wipe papers).

Wiping is maintained until no further removal of deposits from the sidesof the beaker is obtained. After wiping, the beaker is allowed to remainat room temperature before weighing again. The increase in weight of thebeaker after the wiping operation is recorded as the amount of varnish,and by difierence from the total deposit, the amount of carbon isobtained.

As pointed out above, the varnish deposits obtained in this laboratorycombustion test correlate satisfactorily with the actual octanerequirement increase obtained in engine field tests with eightlubricants evaluated with the same fuel. Data illustrating thecorrelation are tabulated below in Table I.

The above data show that a substantially linear correlation existsbetween the varnish deposits as determined by the test of the inventionand the equilibrium octane requirement determined in actual engine fieldtests.

The excellent correlation obtained with lubricants No. 5 and 6 indicatesthat this test is also satisfactory for evaluating lubricants containingash-forming additives, a very important consideration in additivescreening.

EXAMPLE II The following is a detailed procedure of the burning of afuel in the test of the invention. A 400 cc. beaker is Weighed on ananalytical balance to the fourth decimal place. The beaker is thenplaced on an accurate laboratory balance (i. e., torsion balance ofaccuracy better than 0.1 gram) and 200 grams of fuel are weighed intothe beaker. The beaker is then placed under the buming hydrogen torch,which is now operated exclusively with secondary air (0.59 cu. ft./min.of H2), in such fashion that the tip of the torch is 3 /2 inches fromthe top of the beaker. The torch tip is at a slight angle (about 15)above the beaker. The time is noted when the beaker is placed under thehydrogen flame, when the yellow luminous flame of the burning gasolineis gone (approximately 20-25 minutes of burning), and when the beaker isdown to dryness (about 12 minutes later). Care should be exercised inuniformly judging the time of dryness of the beaker, at which point thebeaker is finally removed from the hydrogen flame. This is done byremoving the beaker from the hydrogen flame about 15 seconds afterdisappearance of the yellow luminous flame and noting the presence ofliquid or vapor in the beaker. If no liquid or vapor is present, thebeaker is judged dry and set aside for cooling and weighing. If liquidor vapor are present, the beaker is placed back into flame for anadditional 30 to 60 seconds of burning depending on the amount of liquidpresent. This operation is repeated until dryness is obtained.

The contents of the beaker at this stage are composed of carbonaceousand lead deposits on the sides of the beaker and varnish deposits(generally reddish-brown) at the bottom. The beaker should be allowed tocool at room temperature for at least one hour after removal from theflame before weighing on the analytical balance. The increase in weightis the total deposit due to fuel.

Satisfactory reproducibility has been obtained for fuels in this test.This is illustrated by repeated determinations conducted on variousfuels as shown in Table H below.

Table II 200 Grams in Hydrogen Combustion Test, Milligrams Total DepositRun No. Fuel The total deposits obtained in the hydrogen combustion testwith clear fuels correlates with the equilibrium octane requirementobtained with these fuels in actual 15 engine field tests as shown inTable III.

All types of fuels and lubricants including jet fuels, heating oils,diesel fuels, residual fuel oils, etc., may be tested in accordance withthe invention for their cleanliness properties upon burning. These fuelsare all normally liquid. If it is desired to evaluate fuel or lubricantadditives, the same may be incorporated into fuels or lubricants ofknown deposit-forming characteristics and in this form subjected to thetest described above.

This test is also capable of detecting changes in deposit-formingproperties of fuels during storage. For this purpose, the contents ofthe beaker, after determination of the total deposit, are wiped withsuitable soft laboratory wiping paper (e. g., large Kim-Wipe papers), toremove the lightly adhering deposits. The varnish deposits are firmlyadhered to the glass and are not re moved by the wiping. Following thewiping, the beaker is permitted to stand at room temperature for atleast 30 minutes to leak-off static charge, and reweighed. This givesthe weight of varnish formed in the burning process, and by differencefrom the total deposit, the amount of carbonaceous deposit (plus lead,if present) is obtained. Newly prepared leaded motor fuel containingunsaturates or such fuel carefully stored under nitrogen has varnishdeposits in the order of 3.5 to mgs. The varnish deposits graduallyincrease during storage in air and handling in air, as shown by the dataof Table IV below.

Table IV CHANGE OF DEPOSIT-FORMING PROPERTIES OF MOTOR FUEL ON STORAGEAND HANDLING IN AIR 200 Grams of Fuel in Hydrogen Combustion Test Milli-Sample Description grams Deposit In the foregoing examples the bulk ofthe sample to be tested was placed in the beaker and subjected as suchto the hydrogen flame. If desired, the sample may be suppliedcontinuously or in small increments to the beaker exposed to thehydrogen flame. For example, the sample may be added dropwise from aburette, separatory funnel, or similar overhead reservoir while burningis going on.

It will be understood by those skilled in the art that the invention isnot limited to the exact figures given above for flame length, fuelmixture, flame distances, etc. These figures may be different providedthey are maintained constant for all tests of fuels or lubricants.

What is claimed is:

l. The process of testing the utility of combustible materials whichcomprises subjecting a material selected from the group of lubricatingoils and normally liquid fuels to combustion under a clean-burning flamein an open vessel havingsmooth non-absorbing inner surfaces until saidmaterial is burned to a dry combustion residue remaining on saidsurfaces, subjecting said surfaces to light mechanical friction toremove all loosely adhering deposits leaving a firmly adhering depositnot removable by said light mechanical friction, and determining theweight of said firmly adhering deposit, said plane being directed intothe opening of said vessel.

2. The process of claim 1 in which said flame is a hydrogen flame.

3. The process of testing the tendency of lubricating oils to increasethe octane requirement of internal combustion engines which comprisessubjecting a predetermined amount of said oil to combutsion under ahydrogen flame in an open vessel having smooth non-absorbing innersurfaces until said amount of oil is burned to a dry combustion residueremaining on said surfaces, subjecting said surface to light mechanicalfriction to remove all loosely adhering deposits leaving a firmlyadhering deposit not removable by said light mechanical friction anddetermining the weight of said firmly adhering deposit, said flame beingdirected into the opening of said vessel.

4. The process of claim 3 in which said oil contains ash-formingadditives.

5. The process of claim 3 in which said flame is pro duced by burning amixture of hydrogen and primary air.

6. The process of testing the deposit-forming properties of normallyliquid fuels which comprises subjecting a predetermined amount of saidfuels to combustion under a hydrogen flame in an open vessel havingsmooth nonabsorbing inner surfaces until said amount of fuel is burnedto a dry combustion residue remaining on said surfaces, subjecting saidsurfaces to light mechanical friction to remove loosely adheringdeposits leaving a firmly adhering deposit not removable by saidfriction and determining the weight of said firmly adhering deposit,said flame being directed into the opening of said vessel.

7. The process of testing the utility of a material selected from thegroup of lubricating oils and normally liquid fuels which comprisessubjecting said material to combustion under a clean-burning flame in anopen vessel until said material is burned to a dry combustion residueremaining on the walls of said vessel and consisting of a looselyadhering and a firmly adhering portion, removing said loosely adheringportion and determining the weight of said firmly adhering portion, saidflame being directed into the opening of said vessel.

8. The process of testing the utility of a material selected from thegroup of lubricating oils and normally liquid fuels which comprisessubjecting said material to combustion under a clean-burning flame in anopen vessel until said material is burned to a dry combustion residueremaining on the walls of said vessel and consisting of a looselyadhering and a firmly adhering portion, removing said loosely adheringportion and determining the weight of said loosely adhering portion,said flame being directed into the opening of said vessel.

9. The process of testing the utility of a lubricating oil whichcomprises feeding a predetermined amount of said lubricating oil over anextended period of time to an open vessel, subjecting the materialentering said vessel to combustion under a hydrogen flame to burn saidoil as it enters said vessel to a dry combustion residue remaining insaid vessel, said flame being directed into the opening of said vessel,removing said hydrogen flame after said amount has been burned,subjecting the inner surface of said vessel to light mechanical frictionto remove loosely adhering deposits while leaving a firmly adheringdeposit anddetermining the weight of said firmly adhering deposit.

(References on following page) References Cited in the file of thispatent Hamor: Examination of Petroleum, McGraw-Hill Book Co. (1920),pages 104-106. F l 1 M 1 F. d

He 01 anual by Pau Schml t 1951 pages Malllard et al.: AnnalesCombustlble Llqulds, vol. 11,

68-71, published by the Industrial Press, 148 Lafayette 7 St, New York13, N. Y. Pages 1 -2 (1936)- ASTM Standards on Petroleum Products andLubri- 5 cants, November 1950, pages 65-66.

6. THE PROCESS OF TESTING THE DEPOSIT-FORMING PROPERTIES OF NORMALLYLIQUID FUELS WHICH COMPRISES SUBJECTING A PREDETERMINED AMOUNT OF SAIDFUELS TO COMBUSTION UNDER A HYDROGEN FLAME IN AN OPEN VESSEL HAVINGSMOOTH NONABSORBING INNER SURFACES UNTIL SAID AMOUNT OF FUEL IS BURNEDTO A DRY COMBUSTION RESIDUE REMAINING ON SAID SURFACES, SUBJECTING SAIDSURFACES TO LIGHT MECHANICAL FRICTION TO REMOVE LOOSELY ADHERINGDEPOSITS LEAVING A FIRMLY ADHERING DEPOSIT NOT REMOVABLE BY SAIDFRICTION AND DETERMINING THE WEIGHT OF SAID FIRMLY ADHERING DEPOSIT,SAID FLAME BEING DIRECTED INTO THE OPENING OF SAID VESSEL.